Solar control coatings having a layer stack of glass/Si3N4/NiCr/Si3N4 are known in the art, where the metallic NiCr layer is the sole infrared (IR) reflecting layer in the coating. In certain instances, the NiCr layer may be nitrided.
Unfortunately, while such layer stacks with NiCr IR reflecting layers provide efficient solar control and are overall good coatings, they sometimes are lacking in terms of: (a) corrosion resistance to acid (e.g., HCl boil); (b) mechanical performance such as scratch resistance; and/or (c) thermal stability upon heat treatment for tempering, heat bending, or the like (i.e., ΔE* value(s)). For example, a known heat treatable coated article having a layer stack of glass/Si3N4/NiCr/Si3N4 has an undesirably high glass side reflective ΔE* value of above 5.0 after heat treatment (HT) at 625 degrees C. for about ten minutes. This high glass side reflective ΔE* value means that the coated article when HT will not approximately match its non-HT counterpart with respect to glass side reflective color.
Accordingly, there exists a need in the art for a coated article that has improved characteristics with respect to (a), (b) and/or (c) compared to a conventional layer stack of glass/Si3N4/NiCr/Si3N4, but which still is capable of acceptable solar control (e.g., blocking a reasonable amount of IR and/or UV radiation) and/or heat treatment. It is a purpose of this invention to fulfill at least one of the above-listed needs, and/or other needs which will become apparent to the skilled artisan once given the following disclosure.
A recent development by the instant inventor (which is not prior art to the instant application), set forth in U.S. patent application Ser. No. 10/338,878, filed Jan. 9, 2003 (hereby incorporated herein by reference), is the use of a layer stack of glass/Si3N4/NbNx/Si3N4, where the NbNx is used as the IR reflecting layer. This layer stack is advantageous with respect to the aforesaid glass/Si3N4/NiCr/Si3N4 layer stack in that coated articles with the NbNx IR reflecting layer realize improved color stability upon heat treatment (i.e., lower ΔE* values) and/or improved durability.
While coated articles having a layer stack of glass/Si3N4/NbNx/Si3N4 represent improvements in the art, they are sometimes lacking with respect to durability. For example, they sometimes suffer damage when exposed to certain chemicals such as alkaline solutions, e.g., upon exposure to a one hour NaOH boil test for measuring durability.
FIGS. 2-3 illustrate that coatings including sputter coated layer stacks of glass/Si3N4/Nb/Si3N4 (FIG. 2) and glass/Si3N4/NbNx/Si3N4 (FIG. 3) are often damaged by the one hour NaOH boil test (one hour boil in solution including about 0.1 normal NaOH solution—0.4% NaOH mixed with water—at about 195 degrees F.). For the boil test, see ASTM D 1308-87, incorporated herein by reference.
In FIG. 2, there are six samples illustrated, three in the top row and three in the bottom row (all including a metallic Nb layer). The three top row samples were tested in the NaOH boil as coated on a glass substrate (no heat treatment), whereas the three bottom row samples were tested in the NaOH boil only after they were heat treated (HT) in an oven at about 450 degrees C. for 10 minutes. The two samples in the first column (left-most column) had a layer stack of glass/Nb, the two samples in the middle column had a layer stack of glass/Si3N4/Nb (silicon nitride layer is about 50 Å thick), and the two samples in the third column (right-most column) had a layer stack of glass/Si3N4/Nb/Si3N4 (silicon nitride layers each about 50 Å thick). The lower half of each of the six samples was dipped in the NaOH boil, while the top half was not. It can be seen from FIG. 2 that the NaOH boil test severely damaged all six samples which included the metallic Nb layer, even when the metallic layer was covered by a layer of silicon nitride. Thus, it can be seen that coatings with metallic Nb layers are susceptible to damage when exposed to certain chemicals as illustrated by the damage caused by the NaOH boil test shown in FIG. 2.
FIG. 3 is provided for illustrating the results of the same one hour NaOH boil test carried out on layer stacks including a NbNx layer. In FIG. 3, there are six samples illustrated, three in the top row and three in the bottom row (none were heat treated). The three samples in the top row included a NbNx layer sputter-deposited with 8 sccm nitrogen gas flow (using a Nb target), while the three samples in the bottom row included a NbNx layer sputter-deposited with 10 sccm nitrogen gas flow (using the same Nb target). The two samples in the first column (left-most column) of FIG. 3 had a layer stack of glass/NbNx, the two samples in the middle column had a layer stack of glass/Si3N4/NbNx, and the two samples in the third column (right-most column) had a layer stack of glass/Si3N4/NbNx/Si3N4 (silicon nitride layers each about 50 Å thick). The lower half of each sample was dipped in the NaOH boil, while the top half was not. Since none of these samples were heat treated, they should be compared to the upper row samples from FIG. 2.
Referring to FIG. 3, although the damage was not as severe as in FIG. 2, all six NbNx samples in FIG. 3 were visibly damaged due to the NaOH boil test (even those with a protective silicon nitride layer over the Nb nitride layer), while the three bottom row samples and the two left-most upper row samples were the most severely damaged. Thus, it can be seen that coatings with NbNx layers are susceptible to damage when exposed to certain chemicals as illustrated by the damage caused by the NaOH boil test shown in FIG. 3.
Thus, it will be apparent that there exists a need in the art for coated articles which are capable of achieving acceptable solar control performance, and which are also durable upon exposure to certain chemicals (e.g., NaOH boil test).
In certain example embodiments of this invention, a coating or layer system is provided which includes an infrared (IR) reflecting layer comprising niobium chromium (NbCr) and/or niobium chromium nitride (NbCrNx) sandwiched between at least a pair of dielectric layers. In other words, amount(s) of chromium (Cr) are added to the coatings of FIGS. 2-3 according to different embodiments of this invention. Surprisingly, it has been found that the addition of Cr to the coatings of FIGS. 2-3 enables the resulting coated articles to achieve improved corrosion resistance to alkaline solutions such as NaOH, good mechanical performance such as scratch resistance, and/or good color stability (i.e., a low ΔE* value(s)) upon heat treatment (HT) in certain example instances.
Due to its spectral selectivity, niobium chromium (NbCr) and niobium chromium nitride (NbCrNx) provide thermal performance (e.g., IR blocking) similar to NiCr and NbNx, but are surprisingly more durable (e.g., chemically durable) than both NiCr and NbNx. The use of NbCr and/or NbCrNx in an IR reflecting layer surprisingly results in a solar control coating having excellent scratch resistance, and very good resistance to alkaline solutions such as HCl and/or NaOH. Moreover, it has surprisingly been found that in certain example instances the use of NbCr and/or NbCrNx in/as an IR reflecting layer enables the solar control coating to have significantly improved color stability upon HT (e.g., a lower ΔE* value with a given HT time) than the aforesaid conventional coating where metallic NiCr is used as the IR reflecting layer.
A coated article according to an example embodiment of this invention utilizes such a NbCr and/or NbCrNx layer(s) sandwiched between at least a pair of dielectric layers of a material(s) such as silicon nitride or the like. In certain example embodiments of this invention, the NbCr and/or NbCrNx layer is not in contact with any metallic IR reflecting layer (e.g., is not in contact with any Ag or Au layer).
In certain example embodiments of this invention, heat treated (HT) coated articles including a NbCr and/or NbCrNx inclusive IR reflecting layer(s) have a glass side reflective ΔE* value due to heat treatment of no greater than 3.0, more preferably no greater than 2.5, even more preferably no greater than 2.0, and most preferably no greater than 1.8. For purposes of example, the heat treatment (HT) may be for at least about 5 minutes at a temperature(s) of at least about 580 degrees C.
In certain example embodiments of this invention, the Nb:Cr ratio in the NbCr and/or NbCrNx inclusive IR reflecting layer(s) may be from about 0.75 to 50.0 (i.e., there may be from about 0.75 to 50.0 times as much Nb in the layer compared to Cr in the layer, with respect to atomic %). In certain example embodiments, the layer comprising NbCr (nitrided or not) may include from about 1-70 atomic % Cr, more preferably from about 1-30 atomic % Cr, and most preferably from about 3-20 atomic % Cr.
Generally speaking, certain example embodiments of this invention fulfill one or more of the above listed needs by providing a coated article including a coating supported by a glass substrate, the coating comprising: a first dielectric layer; a layer comprising NbCr and/or a nitride of NbCr; a second dielectric layer, wherein said layer comprising NbCr and/or a nitride of NbCr is located between at least the first and second dielectric layers; and wherein said layer comprising NbCr and/or a nitride of NbCr does not contact any metallic infrared (IR) reflecting layer of Ag.